Cold cathode gaseous discharge tubes



United States Patent CoLD CATHonr. Gasnous macminer. TUBES Raymond Richard Bach, North Harrow, England, assignor to Hives Limited, Greenhill Crescent, Harrowon-the-Hili, Engins/rd, a British company Application Aprii 24, 1953, Serial No. 359,839 Claims priority, appiication Stent Britain July 29, 1952 3 Claims. (Cl. 313-197) This invention relates to cold-cathode gas-discharge tubes and is more particularly concerned with tubes of the so-called relay type in which discharge between a cathode and an anode can be initiated by a control potential applied to an associated trigger electrode and in which the glow discharge thus set up is `arranged to be directed outwardly through a wall of the tube whereby the tube may also serve as a visual indicator device.

The object of the invention is to provide an improved form of such tube construction having improved operating characteristics .and capable of being more easily manufactured, particularly under mass production conditions and in very small sizes, for instance, in the so-called subminiature size.

According to the broadest aspect of the invention the tube comprises a cathode of hollow cup-shaped form which is suitably coated upon its inner surface with an emissive material having a low work function, such cathode having an open smaller diameter end and being associated with an anode which is displaced, in an yaxial direction, away from such smaller diameter open end in a direction opposite to that of the larger diameter open end of the cathode which faces outwardly through a wall of the tube envelope. ln a preferred form the further triggering electrode is disposed substantially in or very close to the plane of such smaller diameter open end.

In order that the nature of the invention may be more readily understood constructional embodiments thereof will now be more particularly described by way of exarnple with reference to the accompanying drawings in which:

Figure l is a longitudinal cross-sectional view through one form of indicator tube according to the invention.

Figure 2 is a `transverse cross-sectional View of the tube, taken on the line lI--ll of Figure l.

Figure 3 is a longitudinal cross-sectional view, similar to Figure l, showing a modification, while Figure 4 is a fragmentary view, also similar to Figure 1, showing a further modification.

Referring first to Figures l and 2 the tube shown comprises an envelope 1d of glass `and of tubular form having a circular vcross-section. The envelope is provided with a at Wall 11 at one end lying yin a plane normal to the axis of the tube envelope and has a flattened sealing pinch formation 12 at the other end. An axially directed glass stem 13 extends inwardly from the pinch 12 to a position approximately mid-way of the axial length of the tube and is there provided with an integral flange or button 14. This button 14 forms a mounting support for certain of the electrode parts and is in the shape of a circular disc disposed normal to the axis of the tube and is of a size which nearly fills the bore of the tube.

The cathode 1S of the tube is in the form of a partspherical or part-paraboloidal metal cup having an open bottom region 15 at its smaller diameter end. This cup is disposed coaxially with the tube axis `and has the rim 17 of its larger end close to and parallel with the fiat end wall 11 of the tube whereby the interior of the cup 2,826,711 Patented Mar.. 11, 1958 ICC faces outwardly through such end wall. This cup is supported by two mounting wires 18 which are secured thereto at diametrically opposite points and are anchored at their other ends in the aforesaid button 14 at `diametrically opposite points. One of these wires 18 is continued downwardly below the button 14 as a connecting lead 19 which passes alongside the glass stem 13 and then through the pinch region 12 to form an external connecting lead. The inside surface 20 of the cup 15 is coated with au emissive material having a suitably low work function whereas the outside `surface 21 is suitably treated, for instance, by calorising, to provide a surface layer which nas a high work function.

The glass stem 13 supporting the aforesaid. button 14 is made hollow as shown at 22 for the major part of its length measured from the button 14 towards the pinch region 12 so as to provide a bore coaxial with the tube envelope 10. Within this bore is located the anode electrode 24 comprising a Wire 23 which passes downwardly through the bore 22 and then through the remaining solid portion of the stem and the pinch region 12 to form an external connecting lead. The innermost end of this wire is provided with a tip portion 25 which `constitutes the anode proper. This tip portion has its end surface 27, which faces the smaller diameter open bottom 16 of the :cup-shaped cathode 1S, sunk a few millimetres below the level of the upper surface 2S of the button 14.

A trigger electrode 3i) in the form of a wire ring 31 of approximately the same diameter `as the open bottom 16 of the cup-shaped cathode 15, is located in `a plane which also lies normal to the tube axis yand which is just inside the said open bottom 16 so that the trigger discharge between the triggering electrode and the cathode can be seen from the anode. This ring is supported at this position by a cranked connecting wire 32 which passes through the open bottom 16, in suitably spaced relationship to the edge of the cup-shaped cathode, and is then anchored, as by spot welding, to a wire 33 which is sealed into the aforesaid button 14. This wire 33 is continued downwardly below the button and alongside' the glass stem 13 and passes out through the pinch region 12 as an external connecting lead.

At a point diametrically opposite to the trigger electrode support wire 33, the button 14 carries a further sealed-in support wire 35 which projects below the button towards the pinch end of the tube and carries thereon the customary pellet 36 of gettering material.

The envelope 10 is filled in the usual way, with a suitable inert gas .such as neon or argon or a mixture thereof and is sealed off `by ya laterally `displaced pip 37. All connecting wires, supports and other conductive elements are preferably coated with alumina or other suitable material having a high work function to prevent undesired discharges taking place thereto.

ln operation, a suitable vol-tage, for instance, of the order of 200 V. is applied between the anode 24 and the cathode 15 through an `appropriate current limiting resistor. This voltage is adjusted -to be of such value that no breakdown occurs within the tube between the anode and cathode without the application of a priming potential to the trigger electrode 30. Upon application of a suitable priming voltage, for instance, a pulse of the order of v. amplitude relative to the cathode through a suitable current limiting resistor, a discharge is initiated between the anode 24 and the cathode 15.

The tube thus constitutes an electronic relay tube for use in the usual manner of such devices. By virtue of the cup-shaped formation of the cathode and its treatment on inner and outer surfaces, `a glow discharge is formed within the cup and by the orientation of such cup to present such hollow inner surface for viewing through the end wall 11, the discharge glow thus formed .gun

permits the device to be used also as an indicator lamp.

In the modication shown in Figure 3, the construction of the electrodes and other parts is generally similar to that already described except that, to facilitate manufacture, the stem 13 is no longer made integral with the envelope and the pinch region, but is, instead, made as a separate element 40 with the connecting wire 23 from the anode tip portion sealed into its lower end and then bent at right angles to the tube axis as shown at 41. This bent end portion is spot welded to a separate connecting lead 42 sealed in a lbase element 43 which is initially made separate from the rest of the envelope 10. The flattened pinch formation of the previous embodiment is dispensed with and the various connectingl leads for the `different electrodes are disposed at various points around the centre point of the base element. At the lcentre of the base element the usual sealing-off tip 44 is provided.

With this construction the whole of the electrode assembly mounted upon the stem 40 and its integral button 14 is fabricated as a separate unit and is then connected by welding to the connecting leads sealed into the base element 43 whereafter the rest of the envelope 10 is passed over the structure and the two envelope parts fused together around the circumferential region x.

Figure 3 `also shows a modified location for the wire ring 31 of the trigger electrode 3i) which is, in this example, located in the same plane as the open bottom 16 of the cathode 15.

A variety of other modifications may obviously be made without departure from the scope of the invention. For example, the cath-ode need not be of partspherical or part-paraboloidal shape but instead may be `of truncated lconical form as shown at 46 in Figure 4, while the form of the trigger electrode likewise need not be as shown. Instead, it can be a short cylinder as indicated at 47 in Figure 4 or even as a simple projecting wire. A further possibility resides in the shaping of the cathode members, so far as their end elevation is concerned, to have :distinctively different forms thereby to facilitate differentiation between one indicator tube and another.

I claim:

l. A cold-cathode gas-discharge tube of the relay type comprising an envelope filled with inert gas having a fiat transparent end wall, a hollow circular section cupshaped :cathode within said envelope disposed with the periphery of its larger diameter open end adjacent to and parallel with said end wall surface, said cathode having an open smaller diameter end, a coating of material having a low work function on the inner wall surface of said cathode, a coating of material having a high work function on the outer wall surface of said cathode, .an anode within said envelope in the form of a wire rod coyaxial with said cathode at a posi-tion displaced away from said smaller area end in a direction opposite to that of said end wall of said envelope and a ring-shaped triggering electrode located within said cathode in the immediate vicinity of said smaller open end, said triggering electrode embracing an area not larger than said smaller diameter open end-of said cathode whereby the trigger discharge between it and said cathode can be seen from said anode.

2. A cold-cathode gas-discharge tube of the relay type comprising a tubular glass envelope filled with inert gas having a fiat transparent end wall, a hollow cup-shaped metal cathode within said envelope disposed with the periphery of its larger diameter open end adjacent to and parallel with said end wall surface, said cathode having an open smaller diameter end, a coating of material of low work function on the inner Wall surface `of said cathode, a coating of material having a high work function on the outer wall surface of said cathode, an .anode within said envelope 'in the form of a metal rod coaxial with the centre of said smaller diameter open end of said cathode at a position displaced away from said smaller area end in a direction opposite to that of said end wall of said envelope, an insulating sleeve surrounding said anode and a circular ring-shaped triggering electrode located within said cathode in the plane of said smaller diameter end, said triggering electrode having `a `diameterless than that of said smaller open end of said cathode.

3. A three-electrode `cold-cathode gas-discharge tube for use also as an indicator tube comprising an envelope having an iner-t gas filling and a flat transparent end wall, a hollow cup-shaped cathode within said envelope disposed With the periphery lof its larger diameter open end adjacent to and parallel with said end wall surface, said cathode having an open smaller `diameter end, a coating of material having a low work function on the inner wall surface of said cathode, the outer wall surface of said cathode having a higher work function value than said inner wall surface, an anode within said envelope n the form of a rod coaxial with the centre of said smaller diameter open end of said cathode at a position displaced away from said smaller open end in a direction opposite to that of said end wall of said envelope, an insulating sleeve surrounding said anode rod and a ring-shaped triggering electrode located just within said cathode in a plane parallel with said smaller open end, said triggering electrode having a `diameter not greater than that of said smaller open end of said cathode whereby the trigger discharge between it and said cathode can be seen from said anode.

References Cited in the file of this patent UNITED STATES PATENTS 1,830,163 Gray Nov. 3, 1931 1,840,055 Rentschler Jan. 5, 1932 2,002,551 Schmierer May 28, 1935 2,142,106 Boswau Ian. 3, 1939 2,159,747 Mendenhall May 23, 1939 2,273,958 Holden Feb. 24, 1942 2,331,398 Ingram Oct. 12, 1943 

